1. Field of the Invention
The present invention refers to methods of enhancing the recovery of desired co-products from post fermentation stillage streams and to processes that recover lipid-rich fractions and aqueous fractions rich in organic acids, glycerin and other compounds present in or derivable from the post fermentation broth.
2. Description of the Related Art
Ethanol production using a wide variety of feedstocks has emerged as an alternative for the replacement of fuels such as gasoline in the transportation and other markets. Feedstocks can include starch-containing agricultural products such as corn, wheat and sorghum sugar-based agricultural products derived from sugar cane, sugar beets, etc.; emerging cellulosic- and lignocellulosic-based biomass from agricultural wastes such as corn stover, rice hulls, and lumber operations, and purpose grown plants and organisms such as switchgrass, Panicum virgatum, Miscanthus, trees, brush, algae, and the like.
For starch based ethanol production, the two most common processes in the United States—the dry-grind process and the wet-mill process. Dry-grind facilities represent the majority of the existing corn ethanol plants in the United States and most of which can generally be described as utilizing a process in which 100% of the corn's composition is fed to the fermentation process. Dry-grind facilities have the advantages of lower overall capital cost, 100% of the fermentable feed enters the fermentation reactors, and free lipids from the feed in the fermentation liquids functions as an anti-foaming agent. Corn oil can be removed in a dry-grind facility by several methods including up-front fractionation of the incoming ground corn, mechanical separation from various stillage streams, and solvent extraction from dried byproducts.
In wet-mill facilities the corn is preprocessed and fractionated into different components such as the germs, glutens, and fibers prior to the fermentation process. The germ contains the majority of the corn oil contained in the kernel. The corn oil can be obtained by mechanical extrusion of the germ, and/or by solvent extraction. The advantages of the wet-mill process is that additional by-products can be extracted prior to the fermentation process, but the disadvantages are much higher overall capital cost, less than 100% of the fermentable feed enters the fermentation reactors resulting in lower ethanol production per mass of feed, and increased operating costs for anti-foaming agents.
Realization that the fermentation by-product streams have potential value is well known in the industry. As early as the 1940s, Brown in U.S. Pat. Nos. 2,211,604, 2,221,605, and 2,263,608 referenced the extraction of animal feed and oil extraction and taught autoclaving of stillage streams to enhance filtration and support downstream solvent extraction. In 1953, Strezynski in U.S. Pat. No. 2,663,718 taught the recovery of oil from distillery stillage using a tri-phase separation centrifuge. This art was again discussed by Prevost in publication US2004/0087808 A1 and Cantrell in publication US 2006/0041152 A1, both of which disclose the recovery of a corn oil co-product from stillage streams of dry grind ethanol facilities using centrifuges. As early as 1911 von Laszloffy disclosed in U.S. Pat. Nos. 1,147,767 and 1,147,768 the presence of desirable compounds in waste distillers slop or stillage. In 1993 Kampen, in U.S. Pat. No. 5,177,008 and in its parent applications U.S. patent application Ser. No. 381,179, filed Jul. 18, 1989, and U.S. patent application Ser. No. 136,415, filed Dec. 22, 1987, disclosed a process for the recovery of other desirable compounds including glycerol, succinic acid, lactic acid, and betaine.
With the evolution of the ethanol industry in the United States centrifuges are frequently included in the process to recover crude corn oil from the stillage streams as an additional co-product that can be used for higher value animal feed or feed stock for biodiesel or renewable diesel production. Frequently, these facilities recover a small fraction of the available oil, or recover a low quality product which contains an excessive quantity of solids that must be removed downstream with a series of high cost bulk storage tanks functioning as high volume settling tanks or decanters.